Electron cooling was originally proposed by Budker in 1966. The basis for his proposal came from work done by Spitzer (1956) who showed that warm ions come to equilibrium with cooler electrons in a plasma. Due to the much larger mass of the ion, the final rms speed of the ions is much less than that of the electrons. Budker realized that an electron beam is simply a moving electron plasma. By superimposing an ion beam on a co-moving electron beam, warmer ions are cooled by the electron beam.
In the 1970's electron cooling was demonstrated to be an extremely good way of increasing the phase space density and stored lifetime of proton beams. Cooling times of between one and ten seconds were reported by experiments at Novosibirsk, CERN, and Fermilab. An experiment completed in Middleton, Wis. culminated in the construction of an electron cooler capable of cooling intermediate energy (about 5 GeV) antiproton beams.
Uses of high intensity, low energy ion beams may include the production of energy through fusion interactions. Several nuclear reactions are known to produce much more energy than the energy required to initiate the interaction, and the initiation energy is very low by particle beam standards.
Uses of high intensity, low energy ion beams may also include the generation of photons, neutrons and a variety of nuclear isotopes, with improved efficiency and yield. Neutrons, isotopes, or photons are used in numerous applications. Neutron applications include boron neutron capture therapy, neutron radiography, and particularly, neutron irradiation for explosive detection, contraband detection, corrosion detection, and other types of non-destructive analysis. Isotope applications include positron emission tomography (PET). Photon (or gamma ray) applications include photonuclear interrogation which has been proposed as another means of detecting contraband and explosives. Photonuclear interrogation is also used for medical imaging and other nondestructive analysis of a wide range of materials.
Conventional techniques involve an electron supply device including a cathode to supply electrons, and including electrodes biased positively with respect to the cathode and arranged so as to accelerate the electrons so that they have the same velocity as the ions. Conventional techniques (see U.S. Pat. No. 7,501,640 incorporated by reference in its entirety) also involve a reverse biasing of electrodes within the electron supply device to serve as a first end of a longitudinal trap for background-ions.
Conventional techniques involve an electron collection device including a collection plate, and including electrodes biased negatively with respect to the collection plate and arranged so as to accelerate the electrons into the collection plate, thereby suppressing secondary emission from the collection plate. Conventional techniques (see U.S. Pat. No. 7,501,640) also involve a reverse biasing of electrodes within the electron collection device to serve as a second end of a longitudinal trap for background-ions.
Typically, the last downstream electrode of the electron supply device is at the potential of the surrounding vacuum pipe (which is typically ground potential) and the electron beam drifts at the potential of the vacuum pipe through a single overlap region and into the electron collection device. For low velocity electron cooling applications, the conventional technique results in a long path of travel with the electrons at low velocity which leads to multiple-scattering-induced transverse-velocity-spread increase.
Conventional techniques in electron cooling use a single electron beam and superimpose that electron beam onto a single ion beam in a single overlap region. Particle collisions between the two beams result in ion beam imperfections being transferred to the electron beam. The electron beam is then separated from the ion beam, and the electron beam is then collected in an electron collection device. Typically, solenoidal and torroidal magnetic field production devices are used to guide the electron beam onto the single ion beam, and then into the electron collection device. However, the conventional technique is costly for applications that require cooling of ions in multiple overlap regions. Conventional electron cooling systems require a separate electron beam and its associated production, transport and collection apparatus for each overlap region.
Accordingly, there is a need for an improved method and system for using a single electron beam to provide ion beam cooling in multiple overlap regions.